Characterization of the intragranular water regime within subsurface sediments: pore volume, surface area, and mass transfer limitations

Water Resources Research
By: , and 

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Abstract

Although "intragranular" pore space within grain aggregates, grain fractures, and mineral surface coatings may contain a relatively small fraction of the total porosity within a porous medium, it often contains a significant fraction of the reactive surface area, and can thus strongly affect the transport of sorbing solutes. In this work, we demonstrate a batch experiment procedure using tritiated water as a high-resolution diffusive tracer to characterize the intragranular pore space. The method was tested using uranium-contaminated sediments from the vadose and capillary fringe zones beneath the former 300A process ponds at the Hanford site (Washington). Sediments were contacted with tracers in artificial groundwater, followed by a replacement of bulk solution with tracer-free groundwater and the monitoring of tracer release. From these data, intragranular pore volumes were calculated and mass transfer rates were quantified using a multirate first-order mass transfer model. Tritium-hydrogen exchange on surface hydroxyls was accounted for by conducting additional tracer experiments on sediment that was vacuum dried after reaction. The complementary ("wet" and "dry") techniques allowed for the simultaneous determination of intragranular porosity and surface area using tritium. The Hanford 300A samples exhibited intragranular pore volumes of ~1% of the solid volume and intragranular surface areas of ~20%–35% of the total surface area. Analogous experiments using bromide ion as a tracer yielded very different results, suggesting very little penetration of bromide into the intragranular porosity.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Characterization of the intragranular water regime within subsurface sediments: pore volume, surface area, and mass transfer limitations
Series title Water Resources Research
DOI 10.1029/2010WR010303
Volume 47
Year Published 2011
Language English
Publisher American Geophysical Untion
Publisher location Washington, D.C.
Contributing office(s) Branch of Regional Research-Western Region
Description 19 p.; W10531
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Water Resources Research